The invention relates generally to devices for sensing the angular position of a rotating shaft and, more particularly, to devices for sensing the angular position of a rotating shift member in a transfer case or transmission and providing an analog output.
In motor vehicle drive line components such as transmissions and transfer cases, it is frequently necessary to provide accurate information to associated electronic controllers, readouts or indicators of the current operating position or condition of the device, such as the currently selected gear, overdrive, four-wheel drive, etc.
Both the sensor and the sensed component take many forms. One of the less complex devices is a multi-featured cam which is attached to and moves with a shift rail and which is engaged by a suitable multiple position sensor. As the cam and shift rail translate relative to the sensor, suitable on-off outputs are provided to a controller or readout which interprets or displays the signals as certain gears or operating conditions.
U.S. Pat. No. 5,867,092 utilizes an array of Hall effect sensors and magnets disposed adjacent an apertured plate which translates past the array of sensors. Such a configuration provides multiple outputs and multiple unique combinations of outputs corresponding to numerous small but finite positions of the shift member and thus provides improved definition of the shift member position to associated controllers or equipment.
A common design concern in such devices is the physical proximity of the sensor to the controlled or shifted device. If the sensor is coupled to the shift component by a hard mechanical connection, there is negligible likelihood that the sensor output and the shift component will assume inconsistent states. However, if the sensor is physically remote from the shifted component or operated or controlled through an auxiliary linkage, the possibility exists that the sensor will provide an output indicating that the shift component is in one position while, in fact, it is occupying another. Obviously, the better sensor/shift component designs are those that minimize this problem.
Another design concern may be the complexity of the sensor. Multiple binary, i.e., two position, sensors, through appropriate coding, can provide accurate information of multiple positions of a shift member. However, multiple sensors are accompanied by the possibility of a failure of one of the sensors which, unless appropriate diagnostic systems are included to detect such failures, may result in a controller misinterpreting the supplied data and provide inaccurate shift commands or indications regarding the current status of the shift member.
If, however, a single sensor is utilized to provide an appropriate position indicating signal, the failure of the single sensor, which typically results in either a total loss of signal or a constant level signal, can be relatively easily diagnosed. The present invention is directed to a closely coupled, rotary shift position sensing device having a single sensor.